Application of a novel open-source program for measuring the effects of toxicants on the swimming behavior of large groups of unmarked fish

Additive effects of microplastics on accumulation and toxicity of cadmium in male zebrafish

Microplastics (MPs) have emerged as contaminants of concern because of their ubiquitous presence in almost all aquatic environments. The ecological effects of MPs are complex and depend on multiple factors including their age, size and the ecological matrix. There is an urgent need for multifactorial studies to elucidate their impacts. We measured the effects of virgin and naturally aged MPs, alone, pretreated with cadmium (Cd), or in combination with ionic Cd, on the bioaccumulation of Cd, metallothionein expression, behavior, and histopathology of adult zebrafish (Danio rerio). Zebrafish were exposed to virgin or aged polyethylene MPs (0.1% MPs enriched diets, w/w) or waterborne Cd (50 μg/L) or a combination of the two for 21 days. There was an additive interaction between water-borne Cd and MPs on bioaccumulation in males but not in females, Cd accumulation increased by twofold when water-borne Cd and MPs were combined. Water-borne Cd significantly induced higher levels of metallothionein compared to MPs pre-exposed to Cd. However, Cd-treated MPs caused greater damage to the intestine and liver compared to untreated MPs suggesting that bound Cd could be released or modulate MPs toxicity. We also showed that co-exposure to water-borne Cd and MPs increased anxiety in the zebrafish, compared with water-borne Cd alone, suggesting using microplastics as a vector may increase toxicity. This study demonstrates that MPs can enhance the toxicity of Cd, but further study is needed to elucidate the mechanism.

Real-time determination of water status upon simultaneous zebrafish exposure to sublethal concentrations of CuSO4

Water pollution from commonly occurring contaminants (metals, xenobiotics, etc.) is a serious global problem. Copper is a commonly occurring water contaminant. A variety of physiological and biological methods have been developed to monitor water quality. The assessment of biological responses is an effective method for identifying the harmful effects of contaminants on ecosystems. Fish is a highly recommended animal model in water quality monitoring. Swimming consistency (firmness) and respiratory metabolism (oxygen consumption rate, carbon dioxide excretion rate and respiratory quotient) are essential for fish to maintain body homeostasis toward coping with environmental stress. We exposed zebrafish to different concentrations (Treatment I-0.1 mg/L and Treatment II-1.58 mg/L) of CuSO₄. We have continuously quantified the strength of behavior (swimming consistency) and physiological (respiratory rates) biomarkers for ten days using an online monitoring system of swimming behavior and external respiration. Swimming consistency and respiratory rates of zebrafish (p<0.05) decreased in the CuSO₄-treated groups compared to the control group. Avoidance behavior has led to an endpoint behavior at copperiedus. The time-delayed toxic effect has resulted in CuSO₄ treatment groups. We checked for swimming consistency aberration on the artificial neural array, Self-organizing map (SOM). Circadian rhythms were influenced by prolonged exposure to CuSO₄ toxicity. A concentration- and duration-dependent behavior anomaly was noted in this study. Swimming behavior and respiratory metabolism patterns are sensitive non-invasive stress biomarkers for water quality monitoring studies.

Organophosphorus-based chemical additives induced behavioral changes in zebrafish (Danio rerio): Swimming activity is a sensitive stress indicator

Organophosphorus flame retardants (OPFRs) have been extensively used as chemical additives in polymer based consumer products. Among them, Isopropylphenyl phosphate (IPPP) and tripropyl phosphate (TPP) are predominant, which have potential to cause neuro-toxic effects on non-target organisms. As behavior (swimming activity) response is the first adjustment due to neurotoxic stress on the fitness of fish. In this study, the quantified swimming activity of zebrafish (Danio rerio) under IPPP and TPP exposure in an online monitoring system was investigated to assess the neurotoxin effects under long-term exposure periods, no swimming anomalies were observed in the control group. Whereas, in the OPFR exposures ((treatment I: 5 μg/L and treatment II: 25 μg/L), a series of anomalies were identified. Hyperactivity was shown in IPPP treatment I group (5 μg/L), whereas zebrafish swimming activity was declined throughout the study period in IPPP treatment II (25 μg/L), and TPP groups (5 μg/L and 25 μg/L) when compared to the control group. Circadian rhythm was not affected in the present study. The results of the present study indicated that the fitness of test individuals was a valid biomarker for eco-toxicity assessment under unescapable conditions. Hypoactivity of zebrafish signified the neurotoxic effects of IPPP and TPP. A concentration based improvement in swimming activity was observed under recovery conditions, which suggested that recovery capacity along with toxicity responses could be a comprehensive non-invasive technique to assess the eco-toxicity of waterborne chemicals.

Biochemical and behavior effects induced by diheptyl phthalate (DHpP) and Diisodecyl phthalate (DIDP) exposed to zebrafish

Both Diheptyl-phthalate (DHpP) and Diisodecyl-phthalate (DIDP) were used extensively as plasticizers. Recently, their occurrence in the environmental matrices and human body fluids have been reported. Unfortunately, these phthalate congeners are without basic toxicity profiles. Hence, we studied the toxic effects of both DHpP and DIDP in the median lethal concentration (LC₅₀ 96-h) on zebrafish (Danio rerio). We assessed swimming behavior strength and tissues biomarker responses including total antioxidants capacity (TAOC), transaminases, and acetylcholinesterase (AChE) enzyme. Fish exposed to phthalate congeners (Treatment-I and-II) for 15-days showed alterations on fish swimming behavior and circadian rhythm. At the end of the exposure period, both liver and heart tissue transaminases activities were found to be accelerated in DHpP and DIDP treated fish, when compared to control group. TAOC and AChE activities were found to be decreased in brain, gills, intestine, and muscle tissues of phthalate congeners treated fish than the control group. Alterations observed in the studied biomarkers were concentration-based response. Among treatment groups DHpP showed higher effects. Comparative studies on swimming behavior and biochemical activities were reasonable to know the swimming responses are mediated due to external stress or internal stress. More studies on molecular and biomarkers assessments are warranted on toxicity of emerging contaminants.

Low-concentration exposure to glyphosate-based herbicide modulates the complexes of the mitochondrial respiratory chain and induces mitochondrial hyperpolarization in the Danio rerio brain

Glyphosate (N-phosphonomethyl-glycine) (GLY) is the active ingredient of the most used herbicides in the world. GLY is applied in formulated products known as glyphosate-based herbicides (GBH), which could induce effects that are not predicted by toxicity assays with pure GLY. This herbicide is classified as organophosphorus compound, which is known to induce neurotoxic effects. Although this compound is classified as non-neurotoxic by regulatory agencies, acute exposure to GBH causes neurological symptoms in humans. However, there is no consensus in relation to neurotoxic effects of GBH. Thus, the aim of this study was to investigate the neurotoxic effects of the GBH in the zebrafish Danio rerio, focusing on acute toxicity, the activity and transcript levels of mitochondrial respiratory chain complexes, mitochondrial membrane potential, reactive species (RS) formation, and behavioral repertoire. Adult zebrafish were exposed in vivo to three concentrations of GBH Scout®, which contained GLY in formulation (fGLY) (0.065, 1.0 and 10.0 mg L-1 fGLY) for 7 d, and an in vitro assay was performed using also pure GLY. Our results show that GBH induced in zebrafish brain a decrease in cell viability, inhibited mitochondrial complex enzymatic activity, modulated gene expression related to mitochondrial complexes, induced an increase in RS production, promoted hyperpolarization of mitochondrial membrane, and induced behavioral impairments. Together, our data contributes to the knowledge of the neurotoxic effects of GBH. Mitochondrial dysfunction has been recognized as a relevant cellular response that should not be disregarded. Moreover, this study pointed to the mitochondria as an important target of GBH.

Can fractal methods applied to video tracking detect the effects of deltamethrin pesticide or mercury on the locomotion behavior of shrimps?

Shrimps can accumulate environmental toxicants and suffer behavioral changes. However, methods to quantitatively detect changes in the behavior of these shrimps are still needed. The present study aims to verify whether mathematical and fractal methods applied to video tracking can adequately describe changes in the locomotion behavior of shrimps exposed to low concentrations of toxic chemicals, such as 0.15µgL^-1 deltamethrin pesticide or 10µgL^-1 mercuric chloride. Results showed no change after 1min, 4, 24, and 48h of treatment. However, after 72 and 96h of treatment, both the linear methods describing the track length, mean speed, mean distance from the current to the previous track point, as well as the non-linear methods of fractal dimension (box counting or information entropy) and multifractal analysis were able to detect changes in the locomotion behavior of shrimps exposed to deltamethrin. Analysis of angular parameters of the track points vectors and lacunarity were not sensitive to those changes. None of the methods showed adverse effects to mercury exposure. These mathematical and fractal methods applicable to software represent low cost useful tools in the toxicological analyses of shrimps for quality of food, water and biomonitoring of ecosystems.

Joint toxicity of cadmium and SDBS on Daphnia magna and Danio rerio

Information on joint toxicity is limited. To clarify the joint toxicity and the interactions among toxicants on different aquatic organisms, we investigated the acute toxicity of cadmium and sodium dodecyl benzene sulfonate, two chemicals with high concerns in Chinese waters, on the immobilization of Daphnia magna (D. magna) and the swimming behavior of Danio rerio (D. rerio). Our results illustrated that cadmium and sodium dodecyl benzene sulfonate expressed a synergistic effect on the immobilization of D. magna; and an antagonistic effect on the swimming speed D. rerio, but a synergistic effect on its vertical position in the water column. Based on the observed data, we found the independent action model was more appropriate than the concentration addition model in the prediction of their joint toxicity. Our results gave an example of the joint toxicity investigation, and aided to comprehensive the toxicity action mode of chemical mixtures.

Locomotor and behavioural responses of empire gudgeons (Hypseleotris compressa) exposed to coal mine wastewater

Coal mining generates large quantities of complex effluent and may pose a threat to aquatic wildlife. Despite this, few studies have explored the consequences of exposure to mine wastewater on aquatic organisms, and this is particularly true for the Australian environment. We investigated sub-lethal behavioural responses in a native Australian fish exposed to wastewater from two releasing dams (CMW1 and CMW2) located at an open cut coal mine in Central Queensland. Swimming activity and movement of empire gudgeons (Hypseleotris compressa) were assessed during a two-week exposure using video-tracking software. Increased activity was observed in exposed fish after 7 and 14 days. Specifically, we found a significant increase in the mean velocity and mobility of fish exposed to CMW1 treatments. Exposed fish also spent on average 23% more time in the peripheral zone compared to controls after 14-d exposures. A similar response pattern was observed in fish exposed to CMW2, but differences between treated and control fish did not generally reach statistical significance. Alterations to normal swimming activity and movement patterns can be indicative of a stress response in fish, and could subsequently lead to negative population-level impacts by increasing the conspicuousness of exposed individuals to predators, or by altering foraging abilities. More research is warranted to explore relationships between behavioural and physiological outcomes, including endocrine disruption, and subsequent population-level outcomes in aquatic organisms at risk of exposure to coal process-affected water.

Bioconcentration of phenanthrene and metabolites in bile and behavioral alterations in the tropical estuarine guppy Poecilia vivipara

Quantification of polycyclic aromatic hydrocarbon (PAH) metabolites in fish bile is widely used to evaluate levels of internal PAH contamination in fish, whereas behavioral effects are deemed important to address potential risks to fish populations. The estuarine guppy Poecilia vivipara was exposed for 96h to waterborne phenanthrene at concentrations of 10, 50, 200 and 500μgL(-1). Phenanthrene and metabolites in bile were analyzed by fixed fluorescence at 260/380nm (excitation/emission) wavelengths. Phenanthrene increased in the bile of exposed fish in a dose-dependent pattern, and log bile bioconcentration factors ranged from 4.3 to 3.9 at 10 and 500μgL(-1) phenanthrene, respectively, values that are similar to predicted bioconcentration factors based on phenanthrene Kow. Swimming resistance index was reduced to 81% of control values at 500μgL(-1). Alteration of swimming speed was non monotonic, with a significant speed increase relative to control fish in treatments 50 and 200μgL(-1) phenanthrene, respectively, followed by a speed decrease in fish exposed to 500μgL(-1). However, swimming trajectories of fish exposed to 50, 200 and 500μgL(-1) was altered by the development of a repetitive circular swimming behavior, in contrast to the controls that explored the entire experimental arena. This change in swimming patterns apparently explains the reduction in prey capture rates at 200μgL(-1) phenanthrene. This study provides important information enabling the use of the estuarine guppy P. vivipara to monitor PAH metabolites in bile and its bioconcentration, linking internal exposure with ecologically relevant behavioral effects in the species.

The use of zebrafish (Danio rerio) behavioral responses in identifying sublethal exposures to deltamethrin

Alterations of fish behavioral responses are sensitive indicators to identify accidental chemical pollution. In this research, a series of exposure tests were conducted to investigate behavioral changes of adult zebrafish (Danio rerio) exposed to deltamethrin (DM) in six concentrations of 0, 0.15, 1.5, 3.75, 7.5 and 15 μg/L. Swimming changes in zebrafish were detected at a concentration as low as 1% of the LC(50-24h) within five hours. Hyperactivity was the first response, followed by a second response of fish surfacing. The change patterns of swimming speed in zebrafish were similar in all exposure groups, but the degree increased with increasing concentrations. Swimming speed and depth were altered within the first two hours after exposure, which was regarded as the most vital phase for water quality monitoring. The duration of hyperactivity and the time of zebrafish surfacing were both logarithmically correlated with exposure concentrations, which was helpful to distinguish the level of pollution.

Development of a new method to track multiple honey bees with complex behaviors on a flat laboratory arena

A computer program that tracks animal behavior, thereby revealing various features and mechanisms of social animals, is a powerful tool in ethological research. Because honeybee colonies are populated by thousands of bees, individuals co-exist in high physical densities and are difficult to track unless specifically tagged, which can affect behavior. In addition, honeybees react to light and recordings must be made under special red-light conditions, which the eyes of bees perceive as darkness. The resulting video images are scarcely distinguishable. We have developed a new algorithm, K-Track, for tracking numerous bees in a flat laboratory arena. Our program implements three main processes: (A) The object (bee's) region is detected by simple threshold processing on gray scale images, (B) Individuals are identified by size, shape and spatiotemporal positional changes, and (C) Centers of mass of identified individuals are connected through all movie frames to yield individual behavioral trajectories. The tracking performance of our software was evaluated on movies of mobile multi-artificial agents and of 16 bees walking around a circular arena. K-Track accurately traced the trajectories of both artificial agents and bees. In the latter case, K-track outperformed Ctrax, well-known software for tracking multiple animals. To investigate interaction events in detail, we manually identified five interaction categories; ‘crossing’, ‘touching’, ‘passing’, ‘overlapping’ and ‘waiting’, and examined the extent to which the models accurately identified these categories from bee's interactions. All 7 identified failures occurred near a wall at the outer edge of the arena. Finally, K-Track and Ctrax successfully tracked 77 and 60 of 84 recorded interactive events, respectively. K-Track identified multiple bees on a flat surface and tracked their speed changes and encounters with other bees, with good performance.